U.S. patent number 6,572,789 [Application Number 10/010,021] was granted by the patent office on 2003-06-03 for corrosion inhibitors for aqueous systems.
This patent grant is currently assigned to Ondeo Nalco Company. Invention is credited to John D. Morris, Peter E. Reed, Bo Yang.
United States Patent |
6,572,789 |
Yang , et al. |
June 3, 2003 |
Corrosion inhibitors for aqueous systems
Abstract
A method of inhibiting corrosion in aqueous systems comprising
adding to the system a composition comprising mono, bis and
oligomeric phosphinosuccinic acid adducts and a method of preparing
a composition comprising mono, bis and oligomeric phosphinosuccinic
acid adducts comprising adding hypophosphite to fumaric acid slurry
or solution in water to create a reaction mixture; and effecting a
reaction by introducing a free radical initiator to the reaction
mixture.
Inventors: |
Yang; Bo (Naperville, IL),
Reed; Peter E. (Plainfield, IL), Morris; John D.
(Naperville, IL) |
Assignee: |
Ondeo Nalco Company
(Naperville, IL)
|
Family
ID: |
25241530 |
Appl.
No.: |
10/010,021 |
Filed: |
December 6, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
824492 |
Apr 2, 2001 |
|
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Current U.S.
Class: |
252/389.23;
252/387; 252/400.23; 422/12; 422/15 |
Current CPC
Class: |
C23F
11/167 (20130101); C02F 5/145 (20130101); C23F
14/02 (20130101); C23F 11/173 (20130101); C23F
11/10 (20130101); C09K 8/54 (20130101); C02F
5/14 (20130101); C23F 11/128 (20130101); C09K
5/10 (20130101); C02F 2103/023 (20130101) |
Current International
Class: |
C09K
8/54 (20060101); C07F 9/30 (20060101); C23F
11/167 (20060101); C23F 11/10 (20060101); C07F
9/48 (20060101); C23F 11/173 (20060101); C07F
9/00 (20060101); C02F 5/14 (20060101); C09K
5/00 (20060101); C02F 5/10 (20060101); C09K
5/10 (20060101); C23F 011/167 () |
Field of
Search: |
;252/387,389.23,389.24,397,400.23,400.24,80,82 ;422/12,13,15
;210/699,697 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Anthony; Joseph D.
Attorney, Agent or Firm: Martin; Michael B. Breininger;
Thomas M.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This is a continuation in part of co-pending Ser. No. 09/824,492,
filed Apr. 2, 2001 now abandoned.
Claims
We claim:
1. A method of inhibiting corrosion in aqueous systems comprising
adding to the system a phosphonosuccinic acid composition
comprising mono, bis and oligomeric phosphinosuccinic acid adducts,
wherein the phosphinosuccinic acid composition comprises about 36
to about 49 mole percent bis phosphinosuccinic acid adducts and
about 26 to about 35 mole percent oligomeric phosphinosuccinic acid
adducts.
2. The method of claim 1 wherein the aqueous system is an
industrial aqueous system.
3. The method of claim 1 wherein the industrial aqueous system is a
cooling water system.
4. The method of claim 1 further comprising adding to the aqueous
system an effective amount of one or more ferrous metal corrosion
inhibitors, yellow metal corrosion inhibitors, scale inhibitors,
dispersants, biocides, and industrial aqueous system additives.
Description
FIELD OF THE INVENTION
This invention relates to a new class of phosphinic acid-based
corrosion inhibitors, to methods of preparing the inhibitors and to
use of the inhibitors to inhibit corrosion in ferrous metal aqueous
systems.
BACKGROUND OF THE INVENTION
Ferrous metals, such as carbon steel, are one of the most commonly
used structural materials used in industrial aqueous systems. It is
well known that corrosion of the metal is one of the major problems
in industrial aqueous systems having ferrous metal in contact with
an aqueous solution. Loss of metals due to general corrosion leads
to deterioration of the structural integrity of the system because
of material strength reduction. It can also cause other problems
elsewhere in the system, such as under-deposit corrosion, reduction
of heat transfer efficiency or even blockage of the flow lines due
to the transport and accumulation of corrosion products in places
with low flow rates or geometric limitations.
Corrosion inhibitors can be used to inhibit the corrosion of
ferrous metals in aqueous or water containing systems. These
aqueous systems, include, but are not limited to, cooling water
systems including open recirculating, closed, and once-through
systems; systems used in petroleum production (e.g., well casing,
transport pipelines, etc.) and refining, geothermal wells, and
other oil field applications; boilers and boiler water systems or
systems used in power generation, mineral process waters including
mineral washing, flotation and benefaction; paper mill digesters,
washers, bleach plants, white water systems and mill water systems;
black liquor evaporators in the pulp industry; gas scrubbers and
air washers; continuous casting processes in the metallurgical
industry; air conditioning and refrigeration systems; building fire
protection heating water, such as pasteurization water; water
reclamation and purification systems; membrane filtration water
systems; food processing streams and waste treatment systems as
well as in clarifiers, liquid-solid applications, municipal sewage
treatment systems; and industrial or municipal water distribution
systems.
Localized corrosion such as pitting may pose even a greater threat
to the normal operation of the system than general corrosion
because such corrosion will occur intensely in isolated small areas
and is much more difficult to detect and monitor than general
corrosion. Localized corrosion may cause perforation quickly and
suddenly without giving any easily detectable early warning.
Obviously, these perforations may cause leaks that may require
unscheduled shutdown of the industrial aqueous system. Sudden
failure of equipment due to corrosion could also result in
environmental damage and/or present a serious threat to the safety
of plant operations.
Corrosion protection of ferrous metal in industrial aqueous systems
is often achieved by adding a corrosion inhibitor. For example,
many metallic ion corrosion inhibitors such as CrO.sub.4.sup.2-,
MoO.sub.4.sup.2-, and Zn.sup.2+ have been used alone or in
combination in various chemical treatment formulations. These
inhibitors, however, have been found to be toxic and detrimental to
the environment and their use in open-recirculation cooling water
systems is generally restricted. Inorganic phosphates such as
orthophosphate and pyrophosphate are also widely used. The
inorganic phosphates have been found to contribute to scale
formation (e.g., calcium phosphate, iron phosphate and zinc
phosphate salts) if used improperly.
In order to obtain satisfactory corrosion protection and scale
control at the same time, a robust treatment program and frequent
testing and monitoring to ensure conformance are often required.
Due to changes in water chemistry (e.g., phosphates, pH, Ca.sup.2+,
etc.) or operating conditions (e.g., temperature, flow rate,
polymer dosages, etc.), these requirements may be difficult to
fulfill, especially in systems with a long holding time index
(e.g., >3 days).
"Holding time index" is a term used to define the half-life of an
inert species such as K.sup.+ added to an evaporative cooling
system. Evaporative cooling systems with a long holding time index
put great demand on treatment chemicals as these chemicals must
remain stable and function properly over long periods of time.
Orthophosphate and pyrophosphate are often used together to provide
optimal corrosion protection, especially against carbon steel
pitting corrosion. Orthophosphate is generally considered as an
anodic corrosion inhibitor. Pyrophosphate is considered as a
cathodic corrosion inhibitor.
It is well known that the combined use of an anodic inhibitor and a
cathodic inhibitor could provide substantial synergistic benefits
for reducing both localized (i.e., pitting) and general corrosion.
Unfortunately, pyrophosphate is not stable in cooling water systems
as it reverts to orthophosphate via a hydrolysis process. The
reversion rate depends on many factors including system holding
time index, temperature, pH, metal ion concentrations and bacteria
activity. Furthermore, the reversion rate in a system is generally
not predictable. In order to maintain satisfactory corrosion
protection performance, a certain level of pyrophosphate (e.g.,
>1.5 ppm p-PO.sub.4) has to be maintained in the system by
frequent monitoring and activating product feed when the level is
lower than the specified value. Although this approach can be
successful, it has a number of major drawbacks.
The drawbacks include the fact that maintenance of pyrophosphate
increases the dosage demand of polymer dispersant and poses an even
greater threat of phosphate scale formation due to the presence of
higher total inorganic phosphate level in the water, especially
when "upsets" occur. Upsets in the context of the usage herein
refer to unanticipated changes in the concentration of inorganic
phosphate or sudden changes in pH, cycle of concentration and
substantial increase of temperature due to non-steady state
operations in cooling waters. Furthermore, in some systems with
very long holding time index (HTI), maintaining a certain specified
level of pyrophosphate is often impossible with an acceptable
pyrophosphate feed dosage.
Some organic phosphonates, such as
2-phosphono-butane-1,2,4-tricarboxylic acid (PBTC),
1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), and
aminotrimethylene-phosphonic acid (AMP) have also been used
previously as corrosion inhibitors alone or in combination with
other corrosion inhibitors in various chemical treatment
formulations. The effectiveness of these phosphonate base
treatments, however, is generally substantially lower than the
treatments based on inorganic inhibitors.
Some hydroxycarboxylic acids such as gluconic acid, sacharic acid,
citric acid, tartaric acid and lactobionic acid have also been used
in some treatment formulations. The use of these acids, however,
results in a major challenge to control microbiological growth
because these hydroxycarboxylates are easily consumable nutrients
for bacteria growth. In addition, their corrosion inhibition
effectiveness is also much lower than the inorganic corrosion
inhibitors. Therefore, they are typically used in low demand and
easy to treat systems, such as some comfort cooling systems.
U.S. Pat. No. 4,606,890 discloses that 2-hydroxy-phosphonoacetic
acid (HPA) can be used as a corrosion inhibitor in cooling water.
HPA was found to be a much more effective corrosion inhibitor than
HEDP and PBTC (See, A. Yeoman and A. Harris, Corrosion/86, paper
no. 14, NACE (1986)). However, HPA is not halogen stable and it
will revert to orthophosphate in the presence of halogen based
biocides. Since bleach or NaOBr are the most widely used biocides
in cooling water systems, the halogen instability of HPA limits its
application potential and reduces its effectiveness. In addition,
HPA is found to be a relatively ineffective CaCO.sub.3 scale
inhibitor.
In order to address some of the limitations of HPA, an
organophosphonic acid mixture has been used by many as mild steel
corrosion inhibitor in cooling water applications (see, U.S. Pat.
No. 5,606,105). The active ingredients of such inhibitors are a
mixture of organophosphonic acids, H-[CH(COONa)CH(COONa)].sub.n
--PO.sub.3 Na.sub.2, where n<5 and n(mean)=1.4, hereinafter
referred to as "PCAM". This mixture is halogen stable under cooling
water application conditions. In addition, these organophosphonic
acids are said to be a better CaCO.sub.3 scale inhibitor than
HPA.
U.S. Pat. No. 5,023,000 discloses and claims a method for
controlling the deposit of calcium carbonate scale on the
structural parts of a system exposed to alkaline cooling water
containing calcium carbonate under deposit forming conditions. This
patent addresses the shortcomings to two counterpart patents GB No.
1,521,440 and U.S. Pat. No. 4,088,678. These patents disclose the
preparation of monosodium phosphinicobis (succinic acid) and
related compounds. These organophosphinic acid mixtures are
prepared by reacting maleic acid with sodium hypophosphite in the
presence of a water soluble initiator. The optimum molar ratio of
maleic acid to hypophosphite is 2.2. These references make it clear
that further excesses of maleic acid do not result in an improved
product. In contrast with the organophosphonic acids mentioned
above, these mixtures are comprised predominantly of a chemically
different type of organophosphorus compound, namely
organophosphinic acids. The salts of organophosphinic acids are
referred to as phosphinates.
U.S. Pat. No. 5,018,577 discloses the use of a predominantly
phosphinate containing composition in oil well applications,
specifically in squeeze treatments for the prevention and removal
of scale from the surfaces of oil wells and formation adjacent to
the casings of these wells.
Similarly, U.S. Pat. No. 5,085,794 discloses the reaction product
of maleic anhydride, water and a persulfate inhibitor for scale
control noting that the disclosed phosphinnicosuccinic acid
oligomer is the component deemed crucial as the active chelant or
scale inhibitor.
In all of these references citing the use of organophosphinic acids
produced from the reaction of hypophosphite with maleic acid for
control of scale formation, it is the oligomer portion of the
reaction product of the maleic acid, hypophosphite and initiator
which is believed to be the key component for use as a scale
inhibitor. None of these references teaches the use of the reaction
product for a corrosion inhibitor in aqueous systems. Furthermore,
none of these references teaches a means to produce the desired
organophosphinic acids in a simple process that converts
essentially all of the hypophosphite and monomer raw materials into
the desirable organophosphinic acid products.
Given the shortcomings noted above, there is a need for a more
cost-effective corrosion inhibitor--capable of inhibiting both
localized and general corrosion--that is environmentally benign and
halogen stable, can maintain its effectiveness in high stress
(i.e., long HTI, high Ca.sup.2+, etc.) conditions and can also
prevent scale formation.
SUMMARY OF THE INVENTION
We have discovered an innovative and very effective class of
phosphinic acid-based organic corrosion inhibitors. The
phosphinosuccinic acid mixture of this invention has all the
desirable properties of a corrosion inhibitor, and in particular,
is a much more effective corrosion inhibitor than PCAM, a
traditional organophosphonic acid mixture. Under certain
conditions, the phosphinosuccinic acid mixture is also more
effective than MoO.sub.4.sup.2-, VO.sub.3.sup.3- nitrite, HEDP,
PBTC, AMP, polyacrylate, phosphonosuccinic acid, orthophosphate,
pyrophosphate and gluconate. The phosphinosuccinic acid mixture is
also as effective as HPA.
The phosphinosuccinic acid mixture can also be formulated with
other components typically used in cooling water treatment (e.g.,
polymer, orthophosphate, etc.) to provide the most cost-effective
corrosion control.
Accordingly, in its principal aspect, this invention is directed to
a method of inhibiting corrosion in aqueous systems comprising
adding to the system a composition comprising mono, bis and
oligomeric phosphinosuccinic acid adducts.
DETAILED DESCRIPTION OF THE INVENTION
The phosphinic acid-based corrosion inhibitor of this invention are
used to prevent corrosion of ferrous metals in aqueous systems,
preferably industrial water systems including cooling water
systems, petroleum systems or mineral process systems. The
phosphinic acid-based corrosion inhibitors are added to the aqueous
system in an amount of from 0.1 to about 10,000 ppm, preferably
from about 0.2 to 100 ppm.
In a preferred aspect of this invention, the industrial aqueous
system is a cooling water system.
The phosphinic acid-based corrosion inhibitors can be used alone or
in combination with other ferrous metal corrosion inhibitors,
yellow metal corrosion inhibitors, scale inhibitors, dispersants,
biocides, and industrial aqueous system additives. Such a
combination may exert a synergistic effect in terms of corrosion
inhibition, scale inhibition, dispersancy and microbial growth
control.
Representative corrosion inhibitors that can be used in combination
with phosphinic acid-based corrosion inhibitors include, but are
not limited to, phosphorus containing inorganic chemicls, such as
orthophosphates, pyrophosphates, polyphosphates; hydroxycarboxylic
acids and their salts, such as gluconic acids; glucaric acid;
Zn.sup.2+, Ce.sup.2+ ; molybdates, vanadates, and tungstates;
nitrites; carboxylates; silicates; phosphonates, HEDP and PBTC.
Representative yellow metal corrosion inhibitors that can be used
in combination with the phosphinic acid-based corrosion inhibitors
include, but are not limited to, benzotriazole, tolytriazole,
mercaptobenzothiazole, halogenated azoles and other azole
compounds.
Representative scale inhibitors that can be used in combination
with the phosphinic acid-based corrosion inhibitors include, but
are not limited to polyacrylates, polymethylacrylates, copolymers
of acrylic acid and methacrylate, copolymers of acrylic acid and
acrylamide, polymaleic acid, copolymers of acrylic acid and
sulfonic acids, copolymers of acrylic acid and maleic acid,
polyesters, polyaspartic acid, funtionalized polyaspartic acids,
terpolymers of acrylic acid, and acrylamide/sulfomethylated
acrylamide copolymers, HEDP (1-hydroxyethylidene-1,1-diphosphonic
acid), PBTC (2-phosphono-butane-1,2,4-tricarboxylic acid), AMP
(amino tri(methylene phosphonic acid) and mixtures thereof.
Representative biocides that can be used in combination with the
phosphinic acid-based corrosion inhibitors include, but are not
limited to, oxidizing biocides, e.g., Cl.sub.2, NaOCl, Br.sub.2,
NaOBr, chlorine dioxide, ozone, H.sub.2 O.sub.2, sulfamic acid
stabilized chlorine, sulfamic acid stabilized bromine,
bromochlorohydantoin, cyanuric acid stabilized Cl.sub.2 or
Br.sub.2, (e.g., trichloroisocyanurate and sodium bromide mixtures,
dichloroisocyanurate and NaBr mixtures), or nonoxidizing biocides
such as glutaraldehdye, isothiozolines
(5-chloro-2-methyl-4-isothiazoline-5-one and
2-methyl-4-isothioazoline-3-one), DBNPA or
dibromonitropropianamide, terbuthylazine and quaterary amine.
The phosphinic acid-based corrosion inhibitor of this invention is
a composition comprising mono and bis and oligomeric
phosphinosuccinic acid adducts of formulas I and II, respectively,
as well as one or more oligomeric species. While the mono and bis
adducts of formula I and II are represented below as neutral,
organophosphinic acid species, it is understood that the phosphinic
and carboxylic acid groups may also exist in salt form. In addition
to the phosphinosuccinic acids and oligomeric species, the mixture
may also contain some phosphonosuccinic acid derivatived from the
oxidation of adduct I, as well as impurities such as various
inorganic phosphorous byproducts of formula H.sub.2 PO.sub.2.sup.-,
HPO.sub.3.sup.2- and PO.sub.4.sup.3-. ##STR1##
Possible structures for the oligomeric species are proposed in U.S.
Pat. Nos. 5,085,794, 5,023,000 and 5,018,577. In addition, the
oligomeric species may also contain esters of phosphonosuccinic
acid, where the phosphonate group is esterified with a
succinate-derived alkyl group.
The mono, bis and oligomeric components are typically characterized
by a group of peaks in the proton decoupled phosphorus NMR spectrum
in water at pH 5 as follows:
Mono: one peak between 26-29 ppm; Bis: two peaks between 30-35 ppm;
and Oligomer: multiple peaks between 29-33 ppm.
In a preferred aspect of this invention, the bis adduct comprises
from about 20 to about 85 mole percent based on phosphorous of the
composition.
The composition is prepared by (1) adding hypophosphite to a maleic
acid or fumaric acid slurry or solution in water to create a
reaction mixture; and (2) effecting a reaction by introducing a
free radical initiator to the reaction mixture. In the case of a
slurry, the solids content is not critical as long as the slurry
can be mixed. Typically, the slurry has a solids concentration of
about 35-50% by weight.
"Hypophosphite" means hypophosphorous acid or a salt of
hypophosphorous acid such as sodium hypophosphite.
The reaction mixture is optionally heated, preferably at from about
40.degree. C. to about 75.degree. C., following addition of
hypophosphite to affect conversion to the desired phosphinosuccinic
acid adducts in a reasonably short period of time.
The reaction mixture may be partially or totally neutralized with
base. A preferred base is aqueous sodium hydroxide which provides a
slurry comprised of a maleic and/or fumaric acid salts. Other bases
capable of forming salts with fumaric or maleic acid, such as
potassium hydroxide and ammonium hydroxide, may also be used. The
base may be added before, after, or concurrently with the
hypophosphite.
Suitable free radical initiators include persulfates, peroxides and
diazo compounds. A preferred initiator is ammonium persulfate. The
initiator may be added to the reaction mixture all at once or
slowly introduced to the reaction mixture over a period of several
hours. The initiator is preferably introduced to the mixture in an
amount of between about 10 to about 15 mole percent based on
hypophosphite.
In a typical prior art procedure for preparing phosphinic acid
compositions, maleic acid with hypohosphite are used in a ratio of
about 2:1. The reaction products are predominately mono, bis and
oligomeric phosphinosuccinic acid adducts and inorganic phosphates
as described above.
We have unexpectedly discovered that if the reaction is carried out
with fumaric acid (trans 1,4-butanedioic acid) instead of maleic
acid (cis 1,4-butanedioic acid) the ratios of mono, bis and
oligomeric phosphinosuccinic acid adducts are altered, resulting in
a composition that displays more effective corrosion inhibition
properties relative to the composition that is produced when maleic
acid is used under the same reaction conditions.
In particular, the fumaric acid-based process provides a simple
means to increase the amount of bis adduct in the composition and
reduce the amount of byproducts in the composition due to a more
efficient conversion of hypophosphite and fumaric acid raw
materials into the desired phosphinic acids.
To achieve a similar result in the maleic acid process, a suitable
form of maleic acid (such as maleic anhydride) must be added
simultaneously with the initiator over the course of the reaction.
These conditions are undesirable when carried out on a large scale
as they require either the use of specialized equipment to feed a
solid reactant to the reactor, a prolonged manual addition of a
solid reactant that increases worker exposure to the chemical
reactants, or the addition of a comparitively large volume of
monomer solution to the reactor that dilutes the product to
undesirable levels. In addition, the maleic acid-based process
still cannot provide for the efficient conversion of essentially
all of the hypophosphite and monomer (maleic or fumaric acid)
reactants to the desired organophosphorous products.
The complete conversion of hypophosphite is important because it
maximizes the yield of the desired products and minimizes the
amount byproducts comprised of the relatively expensive
hypophosphite and its oxidation products (inorganic phosphite and
phosphate) that can otherwise contribute to scale formation when
the desired products are used to inhibit corrosion in aqueous
systems.
The complete conversion of monomer (maleic or fumaric acid) is
important due to economic considerations (yield maximization) and
due to the propensity for unreacted monomer to precipitate out from
the product mixture to give a physically unstable product. Thus,
the fumaric acid-based process of the instant invention gives a
phosphinosuccinic acid product mixture with optimal corrosion
inhibiting properties in a manner that is more efficient and
effective than previously disclosed processes.
The fumaric acid-based process is, in general, very similar to the
maleic acid-based process except that fumaric acid is used in place
of maleic acid. Preferably, the fumaric acid is produced by
isomerization of maleic acid. More preferably, the fumaric acid is
prepared by hydrolyzing maleic anhydride in aqueous solution to
prepare an aqueous solution of maleic acid which is then isomerized
using heat or a suitable catalyst to form an aqueous solution of
fumaric acid.
The isomerization can be accomplished thermally only at high
temperatures, so a catalyst is usually used to allow the reaction
to proceed under relatively mild conditions. Suitable catalysts for
the transformation include thiourea and mixtures of oxidants and
various bromine compounds. A preferred catalyst is a mixture of a
bromide salt with a persulfate salt (U.S. Pat. No. 3,389,173, Ind.
Eng. Chem. Res. 1991, 30, 2138-2143, Chem. Eng. Process., 30
(1991), 15-20). Preferably, a mixture of sodium bromide and
ammonium persulfate is used to affect this transformation in
aqueous media.
The aqueous fumaric acid solution is then converted to the
phosphinic acid-based corrosion inhibitor of this invention by
addition of hypophosphite and a radical initiator to the fumaric
acid solution as described above. A preferred ratio of fumaric acid
to hypophosphite in the reaction mixture is about>1.75-3.
Preferably, the initiator is added over a period of several hours
while the reaction mixture is heated at about 60.degree. C. The
reaction is then allowed to proceed until the hypophosphite is
almost completely converted to organophosphorous products.
An advantage of this preferred process is that it is more
economical because it allows the use of inexpensive maleic
anhydride as a raw material instead of the more expensive fumaric
acid.
Another advantage of the fumaric acid process is that the total
amount of residual inorganic phosphorous in the product is
typically less than three mole percent based on total
phosphorous.
Accordingly, in another aspect, this invention is directed to a
method of preparing a composition comprising mono, bis and
oligomeric phosphinosuccinic acid adducts comprising: i) adding
hypophosphite to fumaric acid acid slurry or solution in water to
create a reaction mixture; and ii) effecting a reaction by
introducing a free radical initiator to the reaction mixture.
In a preferred aspect, the reaction mixture is prepared by
converting an aqueous maleic acid slurry to an aqueous fumaric acid
slurry.
In another preferred aspect, the reaction mixture has a solids
concentration of about 35-50% by weight.
In another preferred aspect, the reaction mixture is neutralized
with base.
In another preferred aspect, the mole ratio of fumaric acid to
hypophosphite in the reaction mixture is about>1.75-3.
In another preferred aspect, the hypophosphite is selected from the
group consisting of hypophosphorous acid or a salt of
hypophosphorous acid.
In another preferred aspect, the reaction mixture is heated.
In another preferred aspect, the free radical initiator is slowly
introduced to the reaction mixture over a period of several
hours.
In another aspect, this invention is directed to an aqueous
composition comprising mono, bis and oligomeric phosphinosuccinic
acid adducts prepared by: i) adding hypophosphite to fumaric acid
acid slurry or solution in water to create a reaction mixture; and
ii) effecting a reaction by introducing a free radical initiator to
the reaction mixture.
The foregoing may be better understood by reference to the
following Examples, which are presented for purposes of
illustration and are not intended to limit the scope of the
invention.
EXAMPLE 1
A 2.1/1 molar ratio of fumaric acid to hypophosphite is used in
this example. Crushed maleic anhydride briquettes, 75.9 parts, are
added to 104.4 parts water in a 1 liter resin flask equipped with a
mechanical stirrer, condenser, nitrogen inlet, and heater. The
anhydride is allowed to hydrolyze at 40.degree. C. to give a maleic
acid solution. The reaction is then heated to 60.degree. C. and a
solution of sodium bromide (0.16 parts dissolved in 0.20 parts
water) is added, followed immediately by a solution of ammonium
persulfate (0.43 parts dissolved in 1.49 parts water). Within 60
minutes, an exothermic reaction ensues that converts the maleic
acid solution into 183.6 parts of a 49.2 wt. % slurry of fumaric
acid in water as verified by proton NMR.
Sodium hypophosphite monohydrate (38.9 parts) is added to 182.6
parts of a 49.2 wt. % slurry of fumaric acid in water contained in
a 1 liter resin flask equipped with a mechanical stirrer,
condenser, nitrogen inlet, and heater. A solution of ammonium
persulfate (10.9 g dissolved in 36.9 parts water) is then added
over a period of 5 hours while the reaction temperature is
maintained at 60.degree. C. under a nitrogen blanket. The reaction
solution is heated 1-5 hours further, and then adjusted to pH 6
under external cooling with 96.2 parts of a 50% aqueous solution of
sodium hydroxide. Finally, 18 parts water is added. The product,
comprised of salts hypophosphite/fumarate adducts described in the
table below, displays the following molar distribution of
components, determined by phosphorous NMR analysis. The first set
of data represents the average of four reactions run at 400-600 g
scale according to the procedure described above. The second set of
data represents a reaction carried out as described above except
that the fumaric acid slurry is prepared by mixing fumaric acid
with water at a 126 g scale.
Component Mole Percent Phosphinicobis(succinic acid) salts
(Structure II) 48, 45 Phosphinicosuccinic acid salts (Structure I)
17, 24 Phosphonosuccinic acid salts 8, 4 Phosphinicosuccinic acid
oligomer salts (Structure III) 27, 27 Hypophosphite, phosphite, and
phosphate salts <1, <1
EXAMPLE 2
A 2.5/1 ratio of fumaric to hypophosphite is used in this Example.
The reaction conditions are as described in Example 1. The product,
comprised of salts of hypophosphite/fumarate adducts described in
the table below, displays the following molar distribution of
components determined by phosphorous NMR analysis.
Component Mole Percent Phosphinicobis(succinic acid) salts
(Structure II) 49 Phosphinicosuccinic acid salts (Structure I) 7
Phosphonosuccinic acid salts 3 Phosphinicosuccinic acid oligomer
salts (Structure III) 38 Hypophosphite, phosphite, and phosphate
salts <1
EXAMPLE 3
This is a comparative example, using maleic acid instead of fumaric
acid at the same 2.5/1 mole ratio as Example 2. It demonstrates
that the results obtained with fumaric acid are unanticipated. The
first data set is the results obtained in the lab using the general
procedure above, and the second data set is a plant run using the
same mole ratio maleic to fumaric. The general reaction conditions
described in Example 1 are repeated except that maleic acid is
substituted for fumaric acid at the same molar concentration. The
product, comprised of salts of hypophosphite/maleate adducts
described in the table below, displays the following molar
distribution of components determined by phosphorous NMR
analysis.
Component Mole Percent Phosphinicobis(succinic acid) salts
(Structure II) 22, 17 Phosphinicosuccinic acid salts (Structure II)
24, 22 Phosphonosuccinic acid salts 2, 12 Phosphinicosuccinic acid
oligomer salts (Structure III) 43, 35 Hypophosphite, phosphite, and
phosphate salts 5, 8
EXAMPLE 4
This example uses a low 1.75/1 ratio of fumaric to hypophosphite.
It does not yield >30% bis product and has a higher level of
undesirable inorganic phosphorous. The reaction conditions
described in Example 1 are repeated except that a larger amount of
hypophosphite is employed so that the molar ratio of fumaric acid
to hypophosphite is 1.75/1. The product, comprised of salts of
hypophosphite/fumarate adducts described in the table below,
displays the following molar distribution of components determined
by phosphorous NMR analysis.
Component Mole Percent Phosphinicobis(succinic acid) salts
(Structure II) 30 Phosphinicosuccinic acid salts (Structure I) 35
Phosphonosuccinic acid salts 8 Phosphinicosuccinic acid oligomer
salts (Structure III) 22 Hypophosphite, phosphite, and phosphate
salts 6
EXAMPLE 5
This example uses a 2.1/1 ratio of substantially neutralized sodium
fumarate slurry demonstrating that the process works over a wide pH
range by use of a salt fumaric acid. In this case, about 80% of the
fumaric acid carboxylic acids have been converted to the sodium
carboxylate form, and the pH is raised from about 1 to about 6.
Sodium hypophosphite monohydrate (13.0 g) is added to 61.0 of a
49.1 wt. % slurry of fumaric acid in water contained in a 250 ml.
resin flask equipped with a mechanical stirrer, condenser, nitrogen
inlet, and heater. Aqueous 50% sodium hydroxide, 32.1 g, is then
added under mixing and cooling. A solution of ammonium persulfate
(3.6 g dissolved in 6.0 g water) is then added over a period of 5
hours while the reaction temperature is maintained at 60.degree. C.
under nitrogen blanket. The reaction solution is heated 1-5 hours
further, and 6 g water is added. The product, comprised of salts of
hypophosphite/fumarate adducts described in the table below,
displays the following molar distribution of components, determined
by phosphorous NMR analysis.
Component Mole Percent Phosphinicobis(succinic acid) salts
(Structure II) 46 Phosphinicosuccinic acid salts (Structure I) 18
Phosphonosuccinic acid salts 8 Phosphinicosuccinic acid oligomer
salts (Structure III) 26 Hypophosphite, phosphite, and phosphate
salts <1
EXAMPLE 6
Step 1: Monosodium Phosphinocobis(dimethyl succinate)
A 2.1 /1 molar ratio of dimethyl maleate to hypophosphite is used
in this example. Sodium hypophosphite, 7.325 parts, are added to
6.25 parts water and 12.5 parts ethanol in a resin flask equipped
with a magnetic stirrer, condenser, nitrogen inlet, heater and a
dropping funnel. This solution is heated to 80.degree. C. A
solution consisting of 20.75 parts dimethyl maleate, 0.86 parts
benzoyl peroxide (70% solution) and 25 parts ethanol is then added
dropwise to the reaction flask over a period of 4.75 hours. The
reaction mixture is heated for an additional 15 minutes then
cooled. The solvent is removed by rotary evaporation under reduced
pressure.
Step 2: Sodium Phosphinocobis(succinate)
34.5 parts of monosodium phosphinocobis(dimethyl succinate) are
added to 20 parts water and 55.4 parts of a 50% aqueous solution of
sodium hydroxide in a reaction flask equipped with a magnetic
stirrer, condenser, and heater. The reaction is heated to
100.degree. C. and maintained at that temperature for 2 hours. The
product is diluted with 20 parts water and then neutralized with
40.4 parts hydrochloric acid to about pH 6.
The product, comprised of salts of hypophosphite/maleate adducts
described in the table below, displayed the following molar
distribution of components determined by phosphorous NMR
analysis.
Component Mole Percent Phosphinicobis(succinic acid) salts
(Structure II) 88 Phosphinicosuccinic acid salts (Structure I) 9
Phosphonosuccinic acid salts 1 Hypophosphite, phosphite, and
phosphate salts 2
EXAMPLE 7
Electrochemical Tests to determine corrosion rate For Tables 1-3. A
pre-polished carbon steel (mild steel, C1010 or C1008) cylindrical
tube (length=0.5 in, outer diameter=0.5 in, area=5 cm.sup.2) sealed
with MICROSTOP STOP-OFF.TM. lacquer (Pyramid Plastic Inc.) and
installed on a Pine rotator is used as the working electrode. The
electrode is polished with a 600 grit SiC sand paper, washed with
acetone and deionized water, and dried with a piece of clean
Kimwipes.TM. before applying the lacquer. Then the electrode is
placed in the air for .about.15 minutes to allow the paint to dry
before immersion. The counter electrode is two high density
graphite rods. A saturated calomel electrode or a Ag/AgCl electrode
is used as the reference electrode. Solution Ohmic drop is
minimized by placing the small Luggin capillary opening about
1.about.2 mm from the working electrode surface. A.C. impedance
experiments shows that the ohmic drop in the low corrosion rate
conditions (e.g., R.sub.p >3000 ohm cm.sup.2 or<7.about.9
mpy) usually contributed to not greater than 10% of the total
measured polarization resistance (R.sub.p).
Test cells holding 700 ml ((for Table 3, 10.8 liters) solution are
used in the tests. The test solutions are prepared from deionized
water, analytical grade chemicals and chemicals synthesized
according to the method described in this invention. The solution
is aerated and allowed to come to thermal and chemical steady-state
(typically.about.0.5 hours) before immersing the working electrode.
All the openings of the cell are covered with either a rubber plug
or Saran Wrap.TM. to minimize solution loss due to evaporation. The
loss due to evaporation is usually less than 10% in 24 hours. The
bench-top corrosion tests are conducted at
38.degree..+-.0.3.degree. C., or 48.9.degree..+-.0.3.degree.,
unless specified otherwise. A pH controller controlled the pH of
the test solution by feeding either dilute H.sub.2 SO.sub.4 or
CO.sub.2 gas (CO.sub.2 is used only in the tests listed in Table
3). The test solutions are also aerated by purging with air during
the tests.
A Gamry potentiostat and Gamry corrosion software are used to
conduct the electrochemical measurements. After>16 hours
immersion, the polarization resistance of the electrode is
determined by imposing a small overpotential (.+-.15 mV versus
E.sub.corr) on the working electrode and measuring the resulting
current under steady state conditions. Quasi-steady-state
potentiodynamic cathodic and anodic scans (e.g., 0.5 mV/sec) are
conducted immediately after the polarization resistance
measurement. These measurements are commenced at the corrosion
potential and polarized up to 200 mV in either cathodic or anodic
direction. The cathodic branch is recorded first. The anodic scan
is conducted .about.0.5 hours after the completion of the cathodic
scan. The surface area averaged (or general) corrosion rates are
determined from extrapolation of either the anodic branch or
cathodic branch of the linear log(i) versus potential region of the
polarization curve to the corrosion potential or are determined
from the polarization resistance with the use of the Stem-Geary
equation. The Tafel slopes of 200 mV/dec for both anodic and
cathodic polarization curves determined from the average values of
several quasi-steady-state potentiodynamic scans measurements and
prior experience are used to calculate the general corrosion rates
from the measured polarization resistances. The corrosion rates
shown in the Tables 1-3 are calculated as the average of
polarization resistance rate, anodic Tafel and cathodic Tafel
extrapolation rates.
In some cases (i.e., the results in Table 3 and the results at 100
F. in Table 1), the carbon steel electrodes are first prepassivated
in 0.5 wt % sodium benzoate solution for 2 to 20 hr at the test
temperature before immersing in the test cell. No significant
differences (e.g., corrosion rate differences are less than 20-30%
from each other) are noted in the corrosion rates obtained from the
different sample preparation methods described here under
comparable test conditions.
All solutions are prepared by using analytical grade chemicals,
commercially available products, or compounds synthesized according
to the procedure described in the instant invention.
TABLE 1 Corrosion Inhibitor Screening Test Results-Hard Water 360
ppm CaCl.sub.2, 200 ppm MgSO4, 100 ppm NaHCO.sub.3, pH = 8.4,
120.degree. F., 160 rpm; 16 hours immersion Dosage as Active in
Acid MS General Corrosion Compound Form or Stated Rate (mpy) Blank
None 43.50 Orthophosphate 15 ppm as PO.sub.4 17.35 Pyrophosphate 30
ppm as PO.sub.4 11.99 HPA 15 ppm 2.13 30 ppm 2.47 Av. of 3 tests
PCAM 15 ppm 15.43 PCAM 20 ppm 6.26 PCAM 30 ppm 23.68 PCAM 40 ppm
15.28 Av. of 6 tests Example 1 15 ppm 2.78 Example 1 20 ppm 2.16
Example 1 30 ppm 0.97 Example 1 40 ppm 2.17 Av. of 2 tests HEDP 15
ppm 13.05 HEDP 30 ppm 8.09 AMP 15 ppm 9.25 AMP 30 ppm 16.11 PBTC 15
ppm 6.17 PBTC 30 ppm 10.49 Polyacrylate 15 ppm 11.84 (MW = 2000)
Polyacrylate 30 ppm 34.49 (MW = 2000) Molybdate 15 ppm as MoO.sub.4
19.89 Vanadate 15 ppm as VO.sub.3 17.43 Nitirte 30 ppm as NO2 9.38
Zn.sup.2+ 5 ppm as Zn 37.24 Gluconate 30 ppm 5.69 Phsophonosucc 15
ppm 6.80 inic acid Blow results are obtained at 100.degree. F.
Blank None 21.5 Av. of 2 tests Example 1 40 ppm 0.98 Av. of 2 tests
Example 1 + 40 ppm Example 1 + 0.92 Av. of 3 Polymer 1 10 ppm
Polymer 1 tests PCAM + 40 ppm PCAM + 19.50 Av. of 3 Polymer 1 10
ppm Polymer 1 tests Note: HPA = 2-hydroxy-phosphonacetic acid PCAM
= phosphonocarboxylic acid mixture, H--[CH(COOH)CH(COOH)].sub.n
--PO.sub.3 H.sub.2, where n < 5 and n.sub.mean = 1.4 HEDP =
1-hydroxyethylidene-1,1-diphosphonic acid AMP = Amino tri(methylene
phosphonic acid) PBTC = 2-phosphono-butane-1,2,4-tricarboxylic acid
Polymer 1 = Acrylic acd (50-60 mole %)/acrylamide (20-36 mole
%)amino methane sulfonate (14-20%) terpolymer
The results in Table 1 show that the compounds of this invention
(i.e., example 1) are much more effective mild steel corrosion
inhibitors than PCAM. The compound of Example 1 is also more
effective than MoO.sub.4.sup.2-, VO.sub.3.sup.3-, nitrite, HEDP,
PBTC, AMP, polyacrylate, phosphonosuccinic acid, o-PO.sub.4,
p-PO.sub.4 and gluconate. It is as effective as HPA. In the
presence of a phosphate dispersant polymer (polymer 1, commonly
used in cooling water systems to prevent scale formation). The
compound of Example 1 is still a more effective mild steel
corrosion inhibitor than PCAM.
TABLE 2 Corrosion Inhibitor Screening Test Results: The Effect
Composition Changes Treatment Composition (based on P.sup.31 NMR
Results) MS General Corrosion Rate (mpy) Mono Adduct Bis adduct
Oligomer 15 ppm 30 ppm Treatment ID (%) (%) (%) Ing P (%) PSA (%)
Treatment Treatment Note A 34 17 35 8 5 11.9 17.7 B 66 15 0 18 1
11.8 3.16 C 65 15 0 20 0 5.72 5.78 D (example 1) 15 49 28 <1 7
2.78 0.97 E 19 45 29 1 6 2.16 2.17 (20 ppm) (40 ppm) F 0 43 27 0 27
2.69 N/A 3% Unidentified G 0 0 60 3 31 21.1 9.2 6% Unidentified H 9
0 56 4 15 6.9 12.2 18% Unidentified PSA 0 0 0 0 100 6.8 27.1 PCAM 0
0 0 0 60 15.4 23.6 Blank 0 0 0 0 0 43.5 Hard Water: 360 ppm
CaCl.sub.2, 200 ppm MgSO.sub.4, 100 ppm NaHCO.sub.3, (all as
CaCO.sub.3), pH = 8.4, 120F, 160 rpm, 16 hours immersion
TABLE 3 Corrosion Inhibitor Screening Test Results: The Effect of
Composition Changes Conditions: 40 ppm total inhibitor
concentration except for the blank test, which has no inhibitor
C1008 Electrode, 360 ppm CaCl2, 200 ppm MgSO4, 100 ppm NaHCO3, (all
as CaCO3), pH = 8.4, 100F, 160 rpm, 24-72 hours immersion.
Treatment Composition based on P31 NMR results MS General Mono
Adduct Corrosion Rate Treatment (%) Bis adduct (%) Oligomer (%) Ing
P (%) PSA (%) (mpy) I 25 36 31 1.2 7 0.98 J 15.9 42 34.6 0.8 6.7
1.82 D (Example 1) 15 49 28 <1 7 1.36 50% D + 50% K 12 68.7 14
1.3 4 2.70 25% D + 75% K 10.5 78.6 7 1.2 2.5 1.83 K 9 88.4 0 1.6 1
7.67 Blank 0 0 0 0 0 21.5
The data in Tables 2 and table 3 show that (1) mixtures of
phosphinosuccinic acid adducts, comprising various percentages of
mono, bis and oligomeric adducts, are effective mild steel
corrosion inhibitor; and (2) the best corrosion inhibition activity
will be obtained if the bis adduct has a percentage ranging from
more than .about.17% to less than 88%.
While the principles of the invention have been shown and described
in connection with but a few embodiments, it is to be understood
clearly that such embodiments are by way of example and are not
limiting.
* * * * *